The present invention relates to a washer used to attach roofing insulation. The washer of the present invention is particularly useful in constructions where single ply roofing membranes are placed over the insulation.
The problem addressed by the present invention involves the puncture of membrane material by fastener heads. This problem arises when screws which are used to secure washers and insulation to a roof substructure become loose and move upward out of their installed positions. Such upward movement is usually attributable to vibration of some sort.
Attempts to eliminate this problem have taken several forms. For example, U.S. Pat. No. 4,361,997 to DeCarro shows engagement between the threads of a screw and the walls of a bore in a washer. Another attempt is the Tap Deck-SP fastener in which an annular ring on the shank of a fastener snaps through the aperture in a washer. A third attempt is shown in FIG. 3 of U.S. Pat. No. 4,074,501 to Sandquist. Sandquist shows a groove formed in a beveled bore. The edges of a countersunk screw head fit into the groove, and tend to prohibit backward motion of the screw.
U.S. Pat. No. 4,380,413 to George G. Dewey, which is owned by the assignee of the present invention, shows a screw and washer combination in which the head of a screw is loosely captivated within a recess in the washer.
It is an object of the present invention to provide a roofing insulation washer which prevents backward motion of a screw during vibration.
Another object of the invention is to provide a washer with means to easily and positively engage the head of a fastener used therewith.
Another object of the present invention is to provide a washer with means for firmly and resiliently gripping the head of a fastener used therewith.
Another object of the invention is to provide a washer in which engagement between the washer and the head of a fastener is easily obtained.